Glow-worm heat exchanger adaptor clip part is located within the heat exchanger section. There are two different types of heat exchanger that can be fitted, the primary heat exchanger and the secondary heat exchanger. The primary is present in almost all boilers and it allows the transfer of heat from the burner to the water within the system. The secondary heat exchanger only appears on combination boilers and allows the heat to be transferred between one closed system and another.